In a current model of the peripheral primate visual system, phasic neurons transmit information about achromatic brightness and border contrast and also about temporal luminescence changes; tonic neurons transmit information about color (hue, saturation and temporal color changes) and about achromatic border contrast. Results presently in the literature suggest an alternate hypothesis: Perception of spatial contours (borders); brightness and color are determined almost exclusively by the tonic system. The primary function of the phasic system is to mediate the perception of temporal luminescence changes; it does not participate significantly in either brightness or spatial vision. I propose to further test and develop this model with a series of psychophysical experiments designed to isolate the tonic and phasic system. Tonic and phasic responses will be distinguished by the selective adaptation and selective sensitivity of each system to specific stimulus parameters. BIBLIOGRAPHIC REFERENCES: Bruce Drum (1976). The relation of apparent brightness to contrast threshold on a photopic background: Dependence on retinal position and target size. Vision Res. 16, 1401-1406. Bruce Drum (1976). Cone latency differences to chromatic stimuli. J. Opt. Soc. Am. 66, 1102-1103. (Abstract of paper presented at 1976 OSA meeting, Tucson, Ariz.).